1. Field Of The Invention
The present invention relates to a compact plasma separator and an apparatus containing the same. More particularly, the present invention is concerned with a compact plasma separator comprising a casing provided with a blood introduction means, a blood withdrawal means and at least one opening for plasma withdrawal and a plurality of porous hollow fibers disposed in the casing, wherein the porous hollow fibers have an average effective length not greater than 200 mm and a membrane surface area not greater than 0.3 m.sup.2, which average effective length is in a specific relationship with an average inner diameter of the porous hollow fibers The present invention is also concerned with an apparatus comprising the above-mentioned compact plasma separator having, connected thereto, a blood introducing passage means, a blood withdrawing passage means and a plasma withdrawing passage means.
By the use of the compact plasma separator and apparatus according to the present invention, effective, efficient separation of whole blood into plasma and blood corpuscles can be attained despite the small size of the plasma separator. A plasma collection rate, as defined later, of 60% or higher, is attained by the use of the compact plasma separator and apparatus according to the present invention.
2. Discussion of Related Art
In recent years, separation of blood by means of porous membranes is increasingly used in the field of medical treatment, in place of the conventional centrifugal separation method. Techniques for separating blood into various blood components according to a membrane separating method are especially used. Among such techniques, the technique using a plasma separator capable of separating blood into corpuscle components and plasma components is utilized for a variety of medical treatment purposes. An example of such medical treatment is found in plasma exchange therapy in which the plasma of a patient suffering from a disease caused by an abnormal plasma component is separated and discarded for replacement with fresh plasma from a healthy person. Another example of such medical treatment is found in plasma purification therapy in which the plasma is separated and purified and then returned to a patient. Further, examples of such medical treatment are found in plasma collection in which only the plasma is collected from a healthy person, and plasma separation from stored blood in which the stored blood is separated into blood corpuscle components and plasma components.
Various proposals have been made in the art for improving plasma collection rate in the separation of whole blood into plasma components and blood corpuscle components using porous membranes. For example, it was proposed to employ a porous membrane having a large surface area, e.g., a porous hollow fiber membrane having a surface area of at least 0.5 m.sup.2. Further, a method in which a plasma collection rate is maximized by increasing the length of a plasma separator having hollow fibers disposed therein has been proposed. A method in which a blood recycle circuit containing a pump therein is provided in an extra-corporeal blood flow circuit comprising a plasma separator so that the blood is recycled through the plasma separator at an increased flow rate has also been proposed. Further, a method in which a porous membrane is rotated at a high speed so as to attain high shear rate has been proposed. However, these conventional methods have drawbacks because the amount of blood to be extracorporeally circulated is large, causing the burden upon the patients or volunteers to be high. Moreover, these conventional methods are disadvantageous because of a danger of hemolysis and because the handling of the apparatus is not easy.
Compact plasma separators are known in the art, which comprise a casing and porous hollow fiber membranes disposed therein. The membranes have a surface area of up to 0.3 m.sup.2 and an average effective length of hollow fibers of up to 200 mm. However, performance for the known compact plasma separators has not been desirable. For example, Plasmapur (trade name of a plasma separator manufactured and sold by Organon Teknika N.V., the Netherlands) comprises a casing and, disposed therein, porous hollow fiber membranes of polypropylene having a membrane surface area of 0.07 m.sup.2, an average effective length of hollow fibers of 150 mm and an average inner diameter of hollow fibers of 330 .mu.m. The plasma collection rate defined later, as measured at a blood flow rate of 100 ml/min using an ACD-added bovine blood with a hematocrit value of 45%, is as low as 47.6%.
U.S. Pat. No. 4,668,399 (also U.S. Pat. No. 4,729,829 being a division of U.S. Pat. No. 4,668,399) discloses a compact plasma separator comprising porous hollow fibers, having a ratio (L/D) of effective length (L cm) to inner diameter (D cm) of not greater than 16,400 cm.sup.-1 D, disposed within a casing having a blood inlet for conducting blood to the fibers, an outlet for conducting exit blood (plasma-depleted blood) from the fibers and a plasma outlet for conducting plasma out of the separator. In the plasma separator of this patent when used in the steady state flow mode, the blood flow rate is low so that the plasma separator exhibits poor plasma collection rate. Therefore, a recycle method and a pulsed flow method are also proposed in the U.S. patent for obtaining an increased yield of plasma, since in such methods, the blood flow rate can be increased. However, the recycle method and pulsed flow method described therein have drawbacks in that the apparatus is not simple, the operation is not easy, and the volume of the blood taken from a patient is inevitably large. Moreover, these methods have drawbacks because hemolysis is likely to occur in a pump for recycling which is employed in the methods, and because blood is likely to contact foreign materials due to the use of a pump for recycling, etc.